Strata

Sedimentary RocksSedimentary Rocks Sedimentary rocks are formed from the Sedimentary rocks are formed from the

breaking apart of other rocks (igneous, breaking apart of other rocks (igneous, metamorphic, or sedimentary rocks) metamorphic, or sedimentary rocks) and the cementation, compaction and and the cementation, compaction and recrystallization of these broken pieces recrystallization of these broken pieces of rock.of rock.

They can also be rocks formed from They can also be rocks formed from sediments or solutionssediments or solutions

Geological processes Geological processes that make and destroy rock:that make and destroy rock: Weathering breaks rock down into fragments called sedimentWeathering breaks rock down into fragments called sediment

WaterWater WindWind IceIce HeatHeat

Deposition is the process by which sediment is Deposition is the process by which sediment is dropped and dropped and comes to restcomes to rest

Erosion is the carrying of that broken up rock or Erosion is the carrying of that broken up rock or sediment by:sediment by:

WaterWater WindWind Ice Ice GravityGravity

Where does sediment come from ?Where does sediment come from ?

Two actions turn sediment into Two actions turn sediment into rock:rock:

Compaction: sediment is squeezed Compaction: sediment is squeezed together by the weight abovetogether by the weight above

Two common cement minerals Two common cement minerals are are quartz and calcitequartz and calcite

Cementation: the sediment is Cementation: the sediment is “glued” “glued” together by mineral material together by mineral material crystallizing between the grainscrystallizing between the grains

Classification of Sedimentary Classification of Sedimentary RocksRocks

Clastic Rocks-Clastic Rocks- Made of the fragments of Made of the fragments of previously existing rockspreviously existing rocks

Sedimentary rocks are classified by the way in which they form:

Organic Rocks-Organic Rocks- Come from organisms Come from organisms Chemical Rocks-Chemical Rocks- Formed by inorganic Formed by inorganic

processes such as evaporationprocesses such as evaporation

Clastic (Detrital) RocksClastic (Detrital) Rocks Clastic sedimentary rocks are formed from Clastic sedimentary rocks are formed from

pieces of sediment cemented together.pieces of sediment cemented together.

Examples of clastic rocks:

• Shale is made of fine, mud-sized grains of sediment.

The grain is so fine that is shows the fine details of fossils.

Shale forms in very still water, as in a lake, swamp or

calm sea. Only in still water can very fine sediment deposit.

• Conglomerate is made of pebbles and is coarse

textured.

• Sandstone is a clastic rock made of sand-sized grains.

Clastic RocksClastic Rocks

Breccia

Conglomerate

Clastic RocksClastic Rocks ConglomerateConglomerate MudstoneMudstone

SandstoneSandstone

Chemical Sedimentary RockChemical Sedimentary Rock Rocks formed when minerals dissolved in Rocks formed when minerals dissolved in

water come out of solutionwater come out of solution

Examples:Examples: GypsumGypsum LimestoneLimestone HaliteHalite

Chemical RocksChemical RocksLimestoneLimestone GypsuGypsu

mmHalite

Organic Sedimentary RocksOrganic Sedimentary Rocks Rocks made from the remains of once-Rocks made from the remains of once-

living organismsliving organisms Some examples:Some examples:

Coal – formed from partially decomposed plant Coal – formed from partially decomposed plant materialmaterial ChalkChalk Limestone -Limestone -• Limestone is formed when pieces of shells from

sea

creatures build up, get compacted and cemented to

form stone.

• Shells or parts of them may be visible as fossils.

Organic RocksOrganic Rocks LimestoneLimestone

CoquinaFossiliferous Limestone

Sedimentary FeaturesSedimentary Features Strata: layers in sedimentary rockStrata: layers in sedimentary rock

oldest oldest layerslayers are generally lower are generally lower

Fossils: any traces or remains of once living Fossils: any traces or remains of once living organismsorganisms They can tell us what organisms lived They can tell us what organisms lived

And what kind of environment was thereAnd what kind of environment was there Mud cracks: which indicate that the mud Mud cracks: which indicate that the mud was was sometimes dried outsometimes dried out Ripple marks: which tell that water or Ripple marks: which tell that water or wind wind was moving over the sedimentwas moving over the sediment

FeaturesFeaturesRipple Marks Mud CracksFossils

Grand Grand CanyonCanyon

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